Updates on locally available COVID-19 vaccines

Published April 13, 2021, 12:20 AM

by Dr. Edsel Salvana

The one on your arm is still your best shot at surviving the pandemic

Dr. Edsel Maurice T. Salvana

Nearly a billion vaccine doses have been given worldwide. There are many encouraging signs that these inoculations will deliver on the promise of ending the pandemic very soon. New cases of COVID-19 have dramatically dropped in Israel and the UK, countries where over half of the adult population has been vaccinated. Meanwhile, many countries in the world, including the Philippines are being threatened by new surges of the more contagious variants.

Despite the rise in cases, more and more healthcare workers have completed their vaccination series. This is a major change from last year when healthcare workers were running scared and desperately running low on PPE. A healthcare workforce that is protected from severe COVID-19 ensures that the people taking care of the sickest COVID-19 patients are no longer in danger of dying from the disease themselves. This is a huge boost to the confidence of our frontliners, and serves as some compensation for bearing the brunt of the pandemic.

A rapid rollout of vaccines in a large number of patients means that even very rare side effects from these injections can emerge. Despite meticulous clinical trials with subjects in the tens of thousands, unusual and uncommon side effects in those with predisposing conditions may be seen on the order of one out of a hundred thousand doses or more. These are exceedingly rare events and may be more coincidental than causative. For instance, the initial rollout of the Pfizer vaccine in Norway was implicated in the deaths of elderly people in nursing homes, prompting a pause in the vaccination of the frail and elderly. This is standard procedure when an unusual cluster of deaths arise. Subsequent investigation showed that this was merely coincidental as the death rate among that population from natural causes is similar to the deaths during vaccination. Nevertheless, warnings were put in place when inoculating the elderly out of an abundance of caution. These pauses for investigation are part of the safety nets for large rollouts of vaccines in order to minimize the risk of harm, given the massive populations being inoculated with relatively new vaccines.

With the administration of nearly one million doses of Astra and Sinovac vaccines in the Philippines, it is worthwhile to review the characteristics of these locally available vaccines, as well as the latest data that is available on their safety and efficacy.

Sinovac

The first vaccine given in the Philippines last March was Sinovac. It was first offered and administered to healthcare workers. There were many reports of mild side effects including arm pain and fatigue, both of which are expected. The vaccinations were generally well-tolerated. A few people developed significant allergic reactions, but these were resolved with supportive care. There were a handful of deaths, not from the vaccine but from other causes, including COVID-19 that was presumably incubating at the time of inoculation.

Newer data out of Turkey from a general population cohort shows that the interim efficacy of Sinovac is 83.5 percent for preventing at least mild disease, and 100 percent were protected from severe disease requiring hospitalization.

The initial Emergency Use Authorization (EUA) excluded seniors 60 years old and above, but over 700 healthcare workers who were seniors chose to be vaccinated anyway. The safety of the vaccine among Filipino seniors does not seem to significantly differ from the general population, and extrapolated efficacy data seems to be acceptable. Sinovac has also been used among seniors in several countries, including Turkey and Indonesia without significant safety signals.

With the delay in release of subsequent Astra vaccines from the WHO COVAX facility, the FDA recently amended the Sinovac EUA to include seniors in order for them to get protection from COVID-19 as soon as possible. There is enough data that Sinovac protects against severe disease in this population. The risk of dying from severe COVID-19 while waiting for another vaccine to arrive amid the tight global supply is higher than the risk of unforeseen side effects from the currently available data. Therefore, in the absence of a viable alternative, the benefit of protection from Sinovac among seniors far outweighs any residual risk that has not been captured by ongoing studies.

Sinovac is a whole inactivated virus vaccine, one of the oldest technologies used for vaccination. Since it uses the whole virus, it generates a multitude of antibodies and may theoretically be more resilient toward variants. The vaccination regimen is two doses, four weeks apart. Full protection is achieved two weeks after the second dose. Recent data from a preprint (non-peer reviewed paper) from Chile suggests limited protection after the first dose, although this was based only on antibody seroconversion data and not actual clinical cases. Nevertheless, it is important to continue adhering to current health standards and prevention measures during and after vaccination until the two-dose regimen is completed. Fully vaccinated individuals can still develop asymptomatic or mild disease and can transmit to others, but will be completely protected from severe disease.

Astra-Zeneca

Astra was the second vaccine rolled out about one week after Sinovac was given. It is the only available vaccine in the Philippines that was initially approved for seniors. Data from the original clinical trials showed a vaccine efficacy of 62 percent against at least mild disease, and 100 percent efficacy against severe disease. Subsequent interim data from clinical trials in the US shows a vaccine efficacy of 76 percent against symptomatic disease and 100 percent efficacy against severe disease. It also reported an 85 percent efficacy against symptomatic disease in those 65 years and older. The initial vaccine schedule was four weeks to 12 weeks apart, but new data suggests that giving the vaccine later may boost efficacy. This is why the second dose for Astra is being delayed for up to three months in the hopes that it will increase the overall efficacy of the vaccine.

A few European countries have recently reported rare blood clots among Astra recipients. After further investigation, the European Medicines Agency (EMA) concluded that it was going to list it as a very rare side effect, on the order of one to five cases out of a million. It did not recommend stopping vaccination, although the UK decided to offer alternative vaccines to those below 30 years old. This is how careful vaccine programs are run all over the world, to ensure that the vaccines remain safe and effective. Review of these findings is ongoing, and the risk versus the benefit of continuing to use Astra in different populations will continue to be assessed. In the meantime, those above 60 years old who are at high risk for dying from COVID-19 will continue to be vaccinated with Astra as the very small risk of rare blood clots is far outweighed by the benefit of protection from severe COVID-19 and death.

In the Philippines, the FDA has momentarily paused the rollout of Astra for those below 60 years old while it studies the implications of the EMA advisory. It continues to allow the use of Astra in those 60 years old and above, as well as the administration of the second dose to those who have already gotten their first dose regardless of age. Since most blood clots occurred after the first dose, the risk of a second dose inducing a rare clot is even smaller. There were no instances of these rare blood clots reported in the initial rollout of the Astra vaccine, but the FDA is being extra cautious. The ongoing review of all vaccines ensures that they remain safe and effective for prevention of severe illness and death from COVID-19.

 
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