AstraZeneca, Pfizer, Moderna, J&J: Differences Between Efficacy and Side Effects of COVID-19 Vaccines


SAN FRANCISCO – Another COVID-19 vaccine, AstraZeneca, is ready to arrive in the US, providing a fourth option for Americans. Each vaccine is given slightly differently, some can cause different side effects, and studies have shown variable efficacy. We are looking at the key differences between the available COVID-19 vaccines, plus the AstraZeneca that is likely approved.

What are the options?

The Pfizer, Moderna, and Johnson & Johnson vaccines have already been cleared for emergency use by the FDA. AstraZeneca is expected to apply for emergency use authorization in the coming weeks.

Which vaccines require one dose and which ones require two doses?

Johnson & Johnson is the only single shot vaccine. All others require two doses at different time intervals. Pfizer suggests that the two doses be given three weeks apart, Moderna suggests four weeks, and AstraZeneca suggests four to 12 weeks.

How effective are vaccines?

In a clinical trial, Pfizer says its vaccine was 95% effective in preventing COVID-19 cases with symptoms and 100% effective when it came to preventing severe cases. Moderna cited similar results, 94% effective.

Johnson & Johnson found that its vaccine, which was tested in the US amid a further increase in COVID-19 transmission, was 72% effective overall and 86% effective in preventing serious diseases.

The most recent US trial shows that the AstraZeneca vaccine was 79% effective in preventing symptomatic COVID-19 cases and 100% effective in stopping severe cases and hospitalization.

Which vaccine is more effective?

One word of caution before comparing the above efficacy rates side by side: clinical trials of the vaccine were conducted under different conditions, which could yield different results. For example, the Johnson & Johnson vaccine was tested in an environment with many more COVID-19 variants circulating and during a time when cases were increasing. The “best” vaccine is the one they offer you, doctors keep reminding the public.

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What are the side effects of each vaccine?

All three approved vaccines have the same common side effects, according to the Centers for Disease Control:

  • Pain, redness, and / or swelling in the arm where you received the injection.
  • Fatigue
  • Headaches
  • Shaking chills
  • Fever
  • Nausea

Concerns about blood clots led several European countries to stop the use of the AstraZeneca vaccine. However, the European Medicines Agency has concluded, after an investigation, that the vaccine does not increase the overall risk of blood clots, but cannot rule out that it is related to two very rare types of clots.

In the most recent American trial of 20,000 people, experts found no increased risk of blood clots.

What vaccines are most common in the US?

According to the CDC, the US has received about 77 million doses of Pfizer, 75 million doses of Moderna, and 4 million doses of J&J at press time. Remember: the J&J vaccine only requires one dose, but it takes two doses of Pfizer or Moderna to fully vaccinate a person.

Can I choose which vaccine to receive?

At this point, no. There may be options in the future, if the supply increases enough.

Associated Press contributed to this report.

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