SINGAPORE - Since receiving the smallpox vaccine as a young boy, Mr Tan Hong San, 78, has become a strong believer in the importance of inoculation to prevent disease.

This was what prompted him to have his Covid-19 shot on Monday (Feb 22) at Senja-Cashew Community Club after receiving his letter last week inviting him to sign up.

After receiving the vaccination, his heart rate increased for a bit but went back to normal within a few minutes.

"I feel okay, normal. I wanted to take a vaccine now rather than later. It's our way of overcoming the pandemic," the retiree told the media.

Mr Tan, who has diabetes and high cholesterol, earlier consulted his family physician, who gave him the green light to take the vaccine.

Those with chronic illnesses such as hypertension, high cholesterol and diabetes, and those with medical co-morbidities who are at risk of serious, life-threatening disease and death from Covid-19 are encouraged to take the vaccine.

Mr Tan was one of many seniors who were inoculated on Monday as Singapore began its nationwide vaccination programme for seniors aged 70 and above.

This next phase in the inoculation drive comes after a pilot in Ang Mo Kio and Tanjong Pagar vaccinated more than 5,000 elderly people in the same age range from Jan 27.

Seniors are at a higher risk of severe disease or complications from Covid-19 infection, and have been prioritised for vaccination.

With three more vaccination centres at community centres and community clubs starting operations by today in Bukit Timah, Marine Parade and Taman Jurong, this brings the total number of vaccination sites in Singapore to 56. They include 14 vaccination centres in the heartland, 20 polyclinics, and 22 Public Health Preparedness Clinics.

By mid-March, 31 vaccination centres will be in operation, with at least one in each town.

In total, there will eventually be around 40 centres, with each planned for an estimated capacity of 2,000 jabs a day.

The 14 vaccination centres are currently open from 9am to 5pm, and will progressively be open from 8am to 10pm.

All seniors will be able to receive their vaccination by mid-March.

By the first week of March , seniors aged 70 and above will receive personalised letters inviting them to sign up for vaccination. Those living near polyclinics or vaccination centres will receive their letters first.

Vaccination for seniors aged 60 to 69 will start from around the end of March, and they will receive their letters from the middle of the month.

The vaccination centre in Senja-Cashew Community Club's sports hall is operated by Thomson Medical, which runs another centre in Bishan Community Club.

Some of the seniors who turned up to receive their shots at Senja-Cashew Community Club on Monday had them deferred until further notice because vaccination was not recommended for them at this time.

People with severely compromised immune systems or a history of anaphylaxis or severe allergic reactions are not advised to take the Covid-19 vaccination. Those who have untreated cancer, or are undergoing treatments such as chemotherapy, should defer vaccination as well.

Some of those whose jabs were deferred at the vaccination centre in Senja-Cashew Community Club had a history of severe drug allergies, said Dr Lin Zhi Yong, the medical officer in charge.

"The vaccine is currently not recommended for those with severe allergic reactions. For these cases, we will defer them from vaccination until further notice from the Ministry of Health," added Dr Lin.

"We will advise these individuals to continue wearing their masks, practise good hand hygiene and encourage those around them to get the vaccination done when their chance comes."

Before the seniors get vaccinated, they have to register and undergo screening, where healthcare workers at the registration counter will ask them about their medical history and questions such as whether they are on blood-thinning medication or if they have food or drug allergies.

"If some of them are unsure about their medical history, we can check the National Electronic Health Record. Some of the residents will bring their own medical records, like their latest blood test reports and medication lists," Dr Lin added.

As at last Thursday, more than 5,000 seniors from Tanjong Pagar and Ang Mo Kio have received their first dose of the vaccine.

Those who had the jab at Senja-Cashew Community Club said they felt good afterwards, and had no adverse reactions. Some of them learnt about the vaccination drive from their children and from the news.

Madam Ng Sam Mui, 74, who took the vaccine with her husband, Mr Tan Kew Sing, 78, said: "I feel safe now after getting the vaccine. There is nothing to be scared about. It's just an injection."

After his jab, cleaner Cheng Choon Kiang, 78, said: "I don't feel anything at all, normal. No pain, nothing. I don't feel feverish. It would be even better once I take the second jab for full protection."

The coffee-shop cleaner added that he plans to encourage his neighbours and co-workers to take the vaccine.

"I meet a lot of people in the coffee shop. I will tell them to come for the jab. I'll show them my jab also," he said, animatedly.

As at last Thursday, about 250,000 people have received their first dose of the Covid-19 vaccine. Of those, more than 110,000 have also received their second dose.

Correction note: In an earlier version of this article, Dr Lin Zhi Yong was quoted as saying the vaccine is currently not recommended for those on blood-thinning medication that causes their platelet level to be too low. The Health Ministry has since clarified that the vaccine is safe for administration for those on blood-thinning medication.