Safety of COVID-19 Vaccines
What you need to know:
• COVID-19 vaccines that are granted with Emergency Use Authorization (EUA) by the Philippine Food and Drug Administration (FDA) are considered safe and effective based on the available evidence to date.
• Vaccines are some of the most rigorously tested medical products today, and the COVID-19 vaccines are no different. The fact that the COVID-19 vaccines are available for use less than a year since the virus was discovered was not because corners were cut in the conduct of the clinical trials.
• COVID-19 vaccines cannot make you sick with COVID-19.
• With BIDA (Bawal walang mask, I-sanitize ang mga kamay, Dumistansya ng isang metrong layo, Alamin ang tamang impormasyon) steps and adherence to the minimum public health standards, vaccination is an important way to protect yourself from getting severe COVID-19.
How Vaccines Work
• Vaccines mimic the virus or bacteria that causes disease and triggers the body’s creation of antibodies. These antibodies will provide protection once a person is infected with the actual disease-causing virus or bacteria.
• Vaccines differ in their composition and how they trigger the immune response to create antibodies. These antibodies protect the body from microorganisms and serve as protection once a person gets infected with disease. Vaccines can be inactivated, weakened or killed copies of the whole or part of the virus or bacteria, or genetic product (like mRNA vaccines) that creates protein copies without causing disease.
WHO defines efficacy as reduction in disease incidence in a vaccinated group compared to an unvaccinated group under optimal conditions such as in a randomized clinical trial.
For COVID-19 vaccine trials, the primary endpoint is the occurrence of symptomatic COVID-19 but they are also measuring other endpoints such as severe COVID, hospitalization due to COVID.
No vaccine provides 100% protection from COVID-19. It typically takes a few weeks for the body to build immunity after vaccination. That means it is possible a person could be infected with the virus that causes COVID-19 just before or just after vaccination and still get sick because the vaccine has not had enough time to provide protection.
In addition, efficacy is measured not only by a vaccine's ability to prevent infection, but also in its prevention of severe forms of the disease and of forward transmission. While a vaccinated person may not be completely prevented from getting infected, s/he will still have a reduced risk of getting severe forms of COVID-19. If more people have this reduced risk, then we can more effectively reduce transmission.
Due to the relatively short observation period for Phase 3 trials, the actual duration of immunity that the vaccines provide is currently unknown. This is still being determined through continuous monitoring of the vaccine recipients in the trials. Until this is established, we must continue practicing minimum public health standards/BIDA behaviors - bawal walang face mask at face shield, i-sanitize ang kamay, dumistansya ng isang metro, at alamin ang tamang impormasyon.
The presence of antibodies can be documented using antibody tests but this is not a requirement post-vaccination and is not recommended based on current evidence particularly for mRNA vaccines.
Emerging data seems to suggest that the current vaccines protect against the new variants. However, definitive studies are still under way to determine whether the vaccines currently being used will protect against the new variants.
A small in vitro study showed that antibodies from people given the BNT162b2 (Pfizer) vaccine were able to neutralize SARS-CoV-2 variants with the N501Y mutation (this was not the UK variant B.1.1.7, which had more mutations). It seems very likely that the other vaccines will result in the same findings, based on expert opinion.
There is currently no evidence on the need for a booster dose/s of the vaccine after the current two-dose vaccine series is complete. The need for and timing of booster doses will be evaluated as further data accumulate.
At this point, only vaccine efficacy (VE) data is available since “effectiveness” depends on many different factors and requires a longer observation period. Further, efficacy data is only available after Phase 3 clinical trials are completed.
- AstraZeneca COVID-19 Vaccine (ChAdOx1-S [recombinant]) VE against symptomatic COVID-19, 14 days after 2nd dose: 70.4% (95% CI 54.8 to 80.6%)
- Pfizer-BioNTech (BNT162b2) VE against symptomatic COVID-19 after 2nd dose: 94.7% (95% CI 90.3 to 97.6%)
- Moderna (mRNA-1273) VE: 94.1% (95% CI 89.3-96.8%)
Clinical trial data show that this varies per individual and that different vaccines have different durations for developing antibodies. Based on available information on reported vaccine efficacy from published Phase III interim results:
1. Pfizer: 7 days after the 2nd dose
2. AstraZeneca: 14 days after the 2nd dose
3. Gamaleya Sputnik V: 21 days after the 1st dose
4. Moderna: 14 days after the 2nd dose
There a lot of factors that can affect vaccine efficacy and age is just one of these factors. Others include:
1. Technology platform used
2. Clinical trial design
3. Health status of clinical trial participants (e.g. presence of comorbidities, HIV-exposure etc. )
4. COVID-19 risk exposure
5. Ethnicity
Hence, when clinical trial results are presented, an overall vaccine efficacy is usually indicated then a vaccine efficacy for the different subgroups (e.g. according to age group, ethnicity) may also be indicated. For the vaccines already approved by Philippine FDA for emergency use, the following are the age groups in which they are allowed to be administered:
1. Pfizer-BioNTech - 16 years old and above
2. AstraZeneca - 18 years old and above
3. Sinovac - 18 to 59 years old
4. Gameleya Sputnik V - 18 years old and above
The EUA terms and conditions can be updated as more clinical trial data becomes available from additional age groups or specific population groups.